Multiple layer coating and cleaning



Jan. 4, 1966 M. ANDERSON ETAL 3,227,133

MULTIPLE LAYER COATING AND CLEANING Filed April 15, 1962 2 Sheets-Sheet 1 VQE/AEL E MAGNET/C POM EB SUPPL Y INVENTORS Mur/A m/pias'om 205:2? 4, 5/1240 Mil/PK! 5, 7/452 Jan. 4, 1966 M. ANDERSON ETAL 3,227,133

MULTIPLE LAYER COATING AND CLEANING Filed April 15 1962 2 Sheets-Sheet 2 Y INVENTORS I G 4 MflIT/N ANDEPJOA/ Pom-Pr 4. sap/we? M4UP/C'FE 7 7Z5? 3)? United States Patent Office 3,227,133 MULTIPLE LAYER COATING AND CLEANING Martin Anderson, Castro Valley, Robert L. Shrader, San

Leandro, and Maurice E. Tyler, El Cerrito, Calif., as-

signors to Temeseal Metallurgical Corporation, Berkeley, Calif, a corporation of California Filed Apr. 13, 1962, Ser. No. 187,341 4 Claims. (Cl. 118-491) The present invention relates to method and apparatus for rapidly and controllably depositing tightly adherent multiple layer coatings of materials upon a substrate in a vacuum.

The deposition of multiple layer coatings upon metals or the like may be accomplished in a variety of ways normally entailing a plurality of processing steps. The present invention provides for cleaning and coating in a high vacuum and utilizes a beam of charged particles both for cleaning the substrate to be coated and for vaporization of the coating material so as to minimize complexity of operations. There is also provided herein for the precise control of initiation and cessation of coating for very accurately controlling the depth of each coating layer. The invention is particularly adapted for the successive coating of layers of different materials upon a single substrate to thereby build up a composite coating of particular desired characteristics.

Although the present invention is widely applicable in the coating of materials, one advantageous ultization of this invention lies in the production of optical filters upon glass or other transparent substrates. Such filters are rapidly and accurately built up by the deposition of successive quarter wave length layers of high and low index of refraction materials, for example, to thereby synthesize particular desired optical characteristics wherein certain wave lengths are highly attenuated and others are little affected. Not only does the present invention provide for a precise control over the degree of coating and also provide for the deposition of multiple layer coatings in a single process, but furthermore there is produced hereby an extremely adherent coating in which the separate layers of the coating are substantially inseparable, and furthermore, in which the coating itself is so bonded to the substrate as to practically form an integral part thereof. In the instance of synthesized light filters attenuating particular portions of the light spectrum, there may be produced an end result in which the coating is so thin as to be unobservable with the naked eye. Further to the foregoing example, it is noted that very complex optical filters may be quite readily and rapidly produced hereby inasmuch as no separate processing is required for the deposition upon the substrate of successive layers of materials of dilferent indices of refraction.

The present invention, in brief, provides for the establishment of a high vacuum in an enclosure and the generation of a controllable beam of charged particles therein. Cleansing of a substrate disposed within the enclosure prior to coating thereof is herein accomplished by the bombardment of the surface thereof with the beam of charged particles. This has proven to be quite advantageous over conventional glow discharge cleansing. Vapor deposition of successive layers of predetermined material upon the substrate is herein accomplished by the bombardment heating of coating material also disposed Within the evacuated enclosure. Precise control over the amount of material deposited is afforded by the provision of a shutter or the like moving in a single direction into intercepting relationship with the vapor and out of intercepting relationship therewith. Furthermore, the invention provides for successively positioning separate materials in the path of the controlled beam of charged par- 3,227,133 Patented Jan. 4, 1966 ticles either by manual control or in response to automatically generated signals.

The apparatus of the present invention includes a movable carrier having indexed positions and adapted to contain coating material for successive positioning of these materials in the path of the bombarding beam for heat-v ing and vaporization of the material. Together with this carrier and within an evacuated enclosure, there is provided means generating and focusing a beam of charged particles such as electrons and a rotatable shutter disposed above the carrier means. A substrate to be coated, such as, for example, glass is also disposed within the evacuated enclosure above the shutter so as to be available for the vapor deposition of materials vaporized from the carrier by the bombarding beam during the. period. in which the shutter does not intercept the rising vapor.

A preferred embodiment of the apparatus of the present invention is illustrated in the accompanying drawings, wherein:

FIGURE 1 is a sectional view taken in a vertical transverse plane through a coating furnace;

FIGURE 2 is a plan view taken in the plane 2--2 of FIGURE 1;

FIGURE 3 is a plan view taken in the plane 3-3 of FIGURE 1; and

FIGURE 4 illustrates as successive portions A, B, C, and D thereof a sequence of precise crucible carrier indexing.

The method of the present invention comprises the steps of disposing a substrate to be coated in a highly evacuated enclosure which is continuously evacuated to a pressure of the order of microns of mercury. Coating materials are disposed Within this chamber for bombardment heating with a beam of charged particles also generated with a high vacuum. A controllable beam focusing is provided to sweep the beam over a substrate for removing impurities therefrom and to direct the beam onto successive coating materials to heat and vaporize same. The vapor so generated rises almost perpendicularly in the high vacuum, and consequently, coats the undersurface of a substrate disposed above the vapor source. Control over the duration of the vapor deposition, in order to obtain coating layers of precise thickness, is afforded by cutting off the flow of vapor in a rapid and controllable manner. Furthermore, the method provides for the control over vapor flow not only as regards cessation of flow, but initiation of flow to the substrate. Consequently, the only vapor reaching the substrate is that which is generated during full generation circumstances. Actuation of the initiation of vapor generation and cessation of same as well as the control over initiation and cessation of vapor flow to the substrate may be accomplished in a variety of manners. Thus, for example, visual observation of interference pat terns may be employed to afford an operator information upon which manual control may be based. Alternatively, there may be employed wholly automatic control and sequencing operations to carry out the above-noted steps of vapor deposition of a plurality of layers of different materials upon a substrate in a high vacuum.

Considering now one particular embodiment of the apparatus in the present invention suitable for carrying out the invention briefly described above, reference is made to FIGURE 1, wherein there is illustrated an enclosure or furnace 21 defining an evacuated chamber 22. A number of large exit ports 23 are provided in this enclosure for connections to high speed pumping means for the rapid and continuous evacuation of the interior of the chamber 22, as indicated by the block arrows 24. Within the evacuated chamber 22 there is disposed means for generating and focusing a beam of charged particles and illustrated as an electron gun 26. Also within the chamber thereis disposeda-crucible carrier 27 having a plurality of crucibles 28 therein which areto be bombarded by an electron beam 29 generated by the gun 26.

Mounting of the foregoing elements is accomplished by the provision of a mounting frame 31 having legs engaging a bottom wall of the enclosure 21 and preferably provided with cooling passages connected to pipes 32 .extending exteriorly of the enclosure to .a source forcirculating a cooling fluid therethrough. The electron gun 26 is disposed atop this frame beside the crucible carrier and includes a backing member 34 having an elongatedopening therein and mounted by an insulating block upon the frame. An electron emissive filament 36 is disposed within the opening in the mounting block of the gun so that upon energization there will be emitted a large quantity of electrons therefrom. An accelerating electrode 37 is disposed adjacent the block above the opening therein and mounted, for example, upon an upright member securedto the top of the frame, so as to extend in part over the opening in the block, as illustrated. Electrons emitted from the filament 36 are accelerated upwardly from the gun in the form of a beam by the accelerating electrode. Establishment of an electron accelerating field is accomplished by the electrical grounding of the ace-aerating electrode 37 and the maintenance of the filament and backing electrode at a highly negative potential. This electrical connection is indicated in FIGURE 1 by a lead extending from the filament and backing electrode in insulating relation through a wall of the enclosure to an external power supply 38.

The above noted crucible carrier 27 is disposed adjacent the electron gun 26 and at least as high as the gun so that the gun is out of the path of vapor rising from the crucibles. The crucible carrier 27 is rotatably mounted for movement between successive indexed positions by a shaft 41 resting upon a thrust bearing in the frame. The shaft 41 extends below the frame and connects by a gear box to a reversing motor 42. Actuation of the motor thus revolves the shaft 41, and consequently, turns the crucible carrier 27 to move the crucibles 28 thereon into and out of indexed positions with respect to the electron gun 26. A crucible shield 43 extends over the top of the crucible carrier and crucibles therein and is provided with a single opening 44 therethrough on the side of the crucible carrier adjacent the electron gun and in position to align with a single crucible disposed beneath this opening. The shield 43 may, for example, be mounted upon the same vertical element mounting as the accelerating electrode 37 of the electron gun, and is formed of a high temperature metal such as tantalum, molybdenum or tungsten. The shield remains immovable While the crucible carrier is rotatably mounted beneath same so as to controllably dispose separate crucibles 28 beneath the opening 44 in the shield, in order that material within these crucibles may be bombardment heated through the shield opening for vaporization of such material.

Control over the electron beam 29 is herein provided by magnetic focusing thereof. A magnet coil 46 is mounted beneath the frame 31 with pole pieces 47 and 48 extending upwardly from the coil ends into the vicinity of the crucible carrier and gun above the frame. The coil 46 is controllably energized from a magnet power supply 49 disposed exteriorly of the enclosure 21 and connected by leads through a wall of this enclosure to the magnet. Variation of magnetic field strength may be obtained by a motor driven rheostat or Variac forming a part of the power supply 49. Energization of the magnet will thus produce a magnetic flux between the pole pieces 47 and 48' associated therewith, and establish a transverse magnetic field in the area through which the electron beam 29 passes. This transverse magnetic field then serves to. curve the trajectory of the beam in proportion to. the strength of the field. The establishment of a magnetic field having the proper field strength will thus serve to produce the electron beam trajectory illustrated in FIGURE 1, wherein the generated beam is curved to pass through the opening 44 in the crucible shield 43 and onto the upper surface of material carried by a crucible 23 disposed immediately beneath this shield opening. The establishment of alternative magnetic field strengths will produce alternative electron beam trajectories, as is discussed in more detail below.

The substrate to be coated by the present invention is disposed within .the evacuated chamber 22 above the crucibles containing the material to be employed for coating the substrate. There is illustrated in FIGURE 1 a plate 51 which is to be coated by material vaporized within the enclosure. A variety of different means may be employed to support the substrate 51 in desired position above the crucibles, and thus the plate or substrate 51 is only illustrated as being positioned as required for vapor deposition. Between the substrate and source of vapor, the present invention provides a shutter 52 having the form, for example, of a generally pear shaped plate mounted upon a vertical shaft 53 extending upwardly from the frame 31 and in rotatable relation thereto. Thus, the shutter 52 may be rotated about the vertical axes of the mounting shaft 53, so as to be controllably disposed between the crucible and substrate. Movement of the shutter 52 is accomplished by a reversing motor 54. mounted beneath the frame 31 and connected to the shaft 53 by appropriate gearing. Energization of this reversing motor 54, as well as the previously noted reversing motor 42. of the crucible carrier, may be provided by an external power supply 56 connected by leads extending in insulated relation through a' Wall of the enclosure 21 into connection with the respective motors.

The preferred embodiment of the present invention described above operates to clean the surface of the substrate to be coated by bombardment of the surface with the electron beam 29 and, furthermore, operates to coat successive layers of different materials upon the substrate by vapor deposition in a high vacuum, This vapor is generated by the electron beam bombardment of material disposed within crucibles of the crucible carrier. The shutter 52 serves to isolate the substrate to be coated from the source of vapor during particular portions of operations, such as indexing of the crucible carrier and initial ieating of the material carried thereby, so as to provide precise control over the amount of material deposited upon the substrate.

Considering now a sequence of operation as may be employed, for example, in the cleaning and multiple coating of glass to form an optical filter thereon, there is first disposed within the chamber 22 a plate of glass 51. Within the crucibles 28 of the crucible carrier 27 there are disposed different materials to be vaporized in the formation of separate layers of the coating to be formed upon the glass substrate. These materials may, in this example, comprise elements or compounds having both low and high indices of refraction and materials such as titanium dioxide and magnesium fluoride may be employed. The vacuum chamber 22 within the enclosure is evacuated to a high degree of vacuum by pumping means connected to the exit ports 23. A very low pressure is maintained within the chamber 22 by continuous evacuation of the chamber throughout vapor deposition of the multiple layer coating. With the shutter 52 rotated to the dashed position thereof in FIGURE 2, i.e. out of alignment with the glass plate 51, the electron gun 26 is energized to pass a current through the filament 36 thereof, so that electrons are emitted therefrom. A suitable accelerating potential is applied to the gun as, for example, by the application of a high negative potential from the power supply 38 to the filament and a grounding of the accelerating electrode 37. This then results in the formation of an electron beam directed upwardly out of the gun structure. The magnetic field established between the pole pieces 46 and 47 associated with the magnet 46' is then varied from a substantially zero value to a higher value so as to sweep the electron beam 29 across the under surface of the substrate 51. It will be seen that a much lower field strength is employed in this beam sweeping than is required to curve the beam into the trajectory illustrated in FIGURE 1. It will be observed by an operator that the bombardment of the glass plate 51 produces a blue glow indicating the removal of impurities therefrom. The beam may be swept back and forth over the under surface of the glass plate until this blue glow disappears, and it is noted at this point that the beam should not be focused into a fine point at the substrate, nor should it be allowed to remain in bombarding relation to any small area of the plate for an extended period of time. Quite clearly, it is possible to melt the plate by the application of sufiicient bombardment energy thereto, however, the apparatus hereof is operated to sweep the beam across the plate by variation of the magnetic field strength so that the plate is not damaged nor over heated by the electron bombardment.

Following the above noted cleaning of the surface of the plate to be coated, the shutter 52 is rotated into the position illustrated in FIGURE 2 of the drawing by actuation of the reversing motor 54, and the crucible carrier 27 is positioned to dispose one crucible 28 immediately below the crucible shield opening 44. With the shield 52 in intercepting relation between the exposed crucible 28 and the cleansed substrate 51, the magnetic field is maintained at a sufficient strength to focus the electron beam 29 through the opening 44 in the shield and thence into the open top of the crucible 28. Within this crucible there is disposed a material to be vaporized and such material is heated to the vaporization temperature by electron bombardment. As the coating material .is being heated by electron bombardment to the point of steady vaporization, the shutter 52 intercepts any spurious vapor molecules that may rise from the material being heated. The shutter motor 54 is then actuated to rotate the shutter shaft 53 and swing the shutter 52 in a counter clockwise direction, as indicated in FIGURE 2,

. away from the substrate 51. The shutter rotates to some non-intercepting position, as for example, through 180 degrees of arc, and remains in this position during the period in which vapor rises from the material in the exposed crucible to deposit upon the under surface of the substrate 51.

Control over the thickness of the deposited layer may be accomplished in a variety of ways, as for example, by manually viewing the coated surface with an interferometer so as to apprise the operator of the thickness and 4 thereby provide him with such information as is necessary to cease vapor deposition of a particular material at such time as the layer ha the desired thickness. In the instance of manual operations such as that briefly noted above, the operator then reactuates the shutter motor to rotate the shutter the remaining 180 degrees of arc, so as to return the shutter to the position of FIGURE 2 in intercepting relationship to vapor arising from the exposed crucible. This manner of shutter movement, i.e. in only one direction, provides for exposing all of the surface of the substrate to the same hidden amount of rising vapor, for the portion first exposed is the portion first hidden by the returning shutter.

With the crucible indexed to the second position, as described above, the accelerating voltage is again applied to the electron gun so that the electron beam 29 again is focused, as illustrated in FIGURE 1, through the opening in the crucible shield 43 and thence onto coating material in the second crucible now disposed beneath the opening 44. The electron beam bombards this material to raise same to vaporization temperature and when such temperature is attained the shutter 52 is again rotated in a counter clockwise direction through about 180 degrees of are so as to exposed the substrate 51 to the vapor rising from the crucible.

As noted above, both of the motors employed for rotatably driving the crucible carrier and the shutter are reversing motors, even though each of these elements are only basically rotated in a single direction. The reversible feature of these motors is herein employed for precise control of the angular position of the shafts attached thereto. This is particularly important as regards the indexing of the crucible carrier, for it will be appreciated to be necessary for the individual crucibles to be precisely located beneath the crucible shield aperture in order for the bombarding electron beam to heat and vaporize material contained in such crucibles. In order to achieve this precise indexing or angular positioning of the crucible carrier, for example, there are provided four radially projecting lugs 61 upon the shaft 41 carrying the crucible carrier. Operating in connection with these lugs is a spring stop 62 formed as a blade extending from a post atop the frame 31. This spring stop 62 has the blade thereof extending toward the shaft 41 slightly off center from the shaft. This arrangement is illustrated in FIG- URE 4, wherein the separate portions A, B, C, and D thereof show the sequence of lug and stop positions during indexing of the crucible carrier upon the shaft. In the position of FIGURE 4A, the shaft is being rotated so that a lug 61 is approaching the spring stop 62. As the shaft continues to rotate, the lug 61 will engage the spring stop and resiliently deflect it, as indicated at FIG- URE 4B. The shaft continues to rotate until it is past the stop, whereat the shaft is then rotated in a reverse direction to move the lug back toward the spring stop, as indicated at FIGURE 4C. Reverse rotation of the shaft may be accomplished by actuation of a reversing switch and limit switch by the shaft lug 61. As the shaft rotates in a reverse direction, the lug 61 thereon will engage the spring stop from the opposite side thereof, and consequently, this spring stop will act as a rigid member because of the normal angular orientation thereof with respect to the shaft. Consequently, the shaft will be stopped and the reversing motor then turned on to leave the shaft in the precise indexed position determined by the relative locations of the lug and spring stop. Although the blade of the spring stop is resilient so as to deflect upon original engagement of the lug therewith, its off-center alignment with the shaft prevents deflection of the blade upon reverse engagement of the lug with the blade. A similar arrangement may be provided upon the shutter shaft 53, however, in this instance it is only necessary to employ two lugs, inasmuch as the shutter itself is rotated between only two positions, as indicated in FIG URE'2.

In accordance with the above sequence of operation, there may be deposited upon the substrate 51 disposed within the evacuated enclosure a plurality of layers of different materials forming a composite coating upon the substrate. The vapor deposition is Very precisely controlled by the apparatus described and invthe manner identified above. The high vacuum existing within the chamber 22 provides for the relatively vertical rise of vapor molecules from the heated coating material, and precise indexing of the crucible carrier is accomplished in order to insure full utilization of the beam energy and to accomplish vaporization of only the material desired for coating.

It will be seen from the foregoing that the illustrated and described apparatus is well adapted to carrying out the coating and cleaning method hereof. While a preferred manner of operation of the apparatus has been described, other modes are possible, and also certain variations of the apparatus are suited for carrying out the coating method. This coating method may, for example, be accomplished by precise refocusing of the bombarding beam into separate crucibles through additional shield apertures or in the absence of a shield. Control of coating thickness may be accomplished manually, as described, or wholly automatically, as by the use of a light source and photocell, for example, to generate control signals. The illustrated apparatus is, however, highly advantageous over alternative structures for multiple coating and cleaning and large scale operations may employ a plurality of coating and cleaning means as described, to thereby uni formly coat extended surfaces.

Although the present invention has been described above in connection with preferred steps and preferred embodiments'of the apparatus of this invention, it will be apparent to those skilled in the art that various modifications and variations are possible. It is thus not intended to limit this invention to the precise terms of the foregoing description, but instead, reference is made to the following claims for a precise definition of the true scope of the invention.

What is claimed is:

1. Multiple layer coating apparatus comprising, a continuously evacuated enclosure having a substrate location therein whereat a substrate is disposed for coating, a movable crucible carrier containing a plurality of crucibles for receiving coating materials positioned substantially beneath the substrate location, an electron gun disposed within saidenclosure below the level of said crucible carrier and laterally spaced therefrom for generating an electron beam, means for focusing the electron beam in a predetermined path, means for moving said crucible carrier to selectively position said crucibles in the path of the electron beam to vaporize coating material in said crucibles, and a movable shutter means mounted between said crucible carrier and the substrate location for selectively blocking the flow of coating material vapors onto the substrate without interrupting the electron beam.

2. Multiple coating apparatus comprising a continuously evacuated enclosure having a substrate location therein whereat a substrate is disposed for coating, a rotatable cruible carrier containing a plurality of crucibles for receiving coating materials positioned substantially beneath the substrate location, a stationary crucible shield having an aperture therein positioned directly above said crucibles, motor means, for rotating said crucible carrier to precisely position said crucibles immediately beneath said aperture,

an electron gun disposed below the level of said crucible carrier and laterally spaced therefrom for generating a high energy electron beam, magnetic field focusing means establishing a controllably variable magnetic field transversely through the path of said electron beam for selectively focusing the electron beam onto the substrate to clean the surface thereof and through said aperture for bombardment heating and vaporization of coating material disposed in said crucible immediately beneath said aperture, and a movable shutter positioned above said crucible shield and out of the path of said electron beam for controlling the deposition of coating material upon the substrate.

3. Multiple coating apparatus comprising a continuously evacuated enclosure having a substrate location therein whereat a substrate is disposed for coating, a rotatable crucible carrier containing a plurality of crucibles for receiving coating materials positioned substantially beneath the substrate location, a stationary crucible shield having an aperture therein positioned directly above said crucibles, motor means for rotating said crucible carrier to precisely position successive crucibles immediately beneath said aperture, said motor means including a shaft driven by a reversing motor integrally connected to said crucible carrier, a plurality of radial lugs upon said shaft, and a spring stop adapted to be engaged by said lugs to stop rotation of said shaft, an electron gun disposed below the level of said crucible carrier and laterally spaced therefrom for generating a high energy electron beam, magnetic field focusing means establishing a controllably variable magnetic field transversely through the path of said electron beam for selectively focusing the electron beam onto the substrate to clean the surface thereof and through said aperture for bombardment heating and vaporization of coating material disposed in said crucible immediately beneath said aperture, and a movable shutter intermediate said crucible shield and the substrate for controlling the deposition of coating material upon the substrate, the shutter being positioned above the path of the electron beam when the beam is focused through said aperture.

4. Multiple layer coating apparatus comprising, a continuously evacuated enclosure having a substrate location therein whereat a substrate is disposed for coating, a movable crucible carrier containing a plurality of crucibles for receiving coating materials positioned substantially beneath the substrate location, an electron gun disposed within said enclosure below the level of said crucible carrier and laterally spaced therefrom for generating an electron beam, means for focusing the electron beam in a predetermined path, means for moving said crucible carrier to selectively position said crucibles in the path of the electron beam to vaporize coating material in said crucibles, and a movable shutter means mounted between said crucible carrier and the substrate location for selectively blocking the flow of coating material vapors onto the substrate without interrupting the electron beam, said shutter including a plate member eccentrically connected to a rotatable shaft, and motor means connected to said shaft for rotation of said shaft and said plate in a circular motion.

References Cited by the Examiner UNITED STATES PATENTS 2,482,329 9/ 1949' Dimmick 118-49 2,746,420 5/1956 Steigerwald 117-106 X 2,932,588 4/1960 Frank 117106 3,046,936 7/1962 Simon's ll349.1

FOREIGN PATENTS 754,102 8/1956 Great Britain.

RICHARD D. NEVIUS, Primary Examiner.

WILLIAM D. MARTIN, Examiner. 

1. MULTIPLE LAYER COATING APPARATUS COMPRISING, A CONTINUOUSLY EVACUATED ENCLOSURE HAVING A SUBSTRATE LOCATION THEREIN WHEREAT A SUBSTRATE IS DISPOSED FOR COATING, A MOVABLE CRUCBLE CARRIER CONTAINING A PLURALITY OF CRUCIBLES FOR RECEIVING COATING MATERIALS POSITIONED SUBSTANTIALLY BENEATH THE SUBSTRATE LOCATION, AN ELECTRON GUN DISPOSED WITHIN SAID ENCLOSURE BELOW THE LEVEL OF SAID CRUCIBLE CARRIER AND LATERALLY SPACED THEREFROM FOR GENERATING AN ELECTRON BEAM, MEANS FOR FOCUSING THE ELECTRON BEAM IN A PREDETERMINED PATH, MEANS FOR MOVING SAID CRUCIBLE CARRIER TO SELECTIVELY POSITION SAID CRUCIBLES IN THE PATH OF THE ELECTRON BEAM TO VAPORIZE COATING MATERIAL IN SAID CRUCIBLES, AND A MOVABLE SHUTTER MEANS MOUNTED BETWEEN SAID CRUCIBLE CARRIER AND THE SUBSTRATE LOCATION FOR SELECTIVELYY BLOCKING THE FLOW OF COATING MATERIAL VAPORS ONTO THE SUBSTRATE WITHOUT INTERRUPTING THE ELECTRON BEAM. 